A child’s tantrum isn’t a function of conscious sin, but environment. Change the environment and a child needn’t throw a tantrum. Ours never did. We noted that every tantrum came from one or a combination of four things: tiredness, hunger, sickness or frustration. It’s an opportunity to learn for both child and parent not evidence of a sinful nature.
I've seen plenty of selfish behavior of 7 & under...
I've seen fights...
Etc.
And your "change the environment" message is not a complete cure-all.